Steerable directional random antenna array



Oct. 2, 1962 G. MITCHELL STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY 4Sheets-Sheet l Filed Aug. l2, 1958 A'r'roRNEY5 Oct. 2, 1962 G. MITCHELL3,056,961

STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY Filed Aug. l2, 1958 4Sheetsiheet 2 INvemoR GEOFf/Qf Y Ml Ter/fu.

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ATTQRN EYS Oct. 2, 1962 G. MITCHELL STEERABLE DIRECTIONAL RANDOM ANTENNAARRAY Filed Aug. l2, 1958 PHASESMFH-'RS w f m 4 INvEN-roR GEOFFREYM/TCHELL #vz/Z n Awww a# 5 Oct. 2, 1962 G. MITCHELL 3,055,961

STERRABLE DIRECTIONAL RANDOM ANTENNA ARRAY Filed Aug. l2, 1,95? 4Sheets-Sheet 4 O OOO /5 O oooooooooooooooooooo A/ y/LA* T K/ 4/ 142 lDG/ 2 Jr(, o/

YTHTT WCHA F/ @L12 I Vm 'l V7 6/\| T P l 'Ti-"- l G/Z o o/G2 i M l Ye i:s l INVENTR H/ (raw-Mey r1 CHELL i 2 /A-m *i i 3,056,951 ICC Patentedoct. 2, 1962 3,056,961 STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY GeoreyMitchell, Boreham Wood, England, assignor to Her Majestys PostmasterGeneral, London, England Filed Aug. 12, 1958, Ser. No. 754,567 Claimspriority, application Great Britain Aug. 15, 1957 3 Claims. (Cl.343-854) The present invention relates to steerable directional aerialsystems using a number of lixed spaced aerials, the directionalproperties in azimuth and elevation of which may be varied electrically,and has for an object to provide such a system which is substantiallyuniversally steerable.

Steerable directional aerial systems are known and one system has beenproposed in which an array of spaced vertical -aerials is provided, theaerials being positioned in :rows to form a square pattern and thesignals from the aerials being combined, after adjustment `for the timedelay differences, by means of variable time delay networks. The outputsof the aerials of each row are fed respectively over equi-lengthco-axial cables to pri' mary variable time delay networks by means ofwhich the signals from the row of aerials are adjusted and combined andthe resultant outputs from the primary networks-equal in number to thenumber of rows of the aerials-are fed to secondary variable time delaynetworks to be further adjusted and combined, the resultant output beingfed to the receiver. The said prior proposal also envisages theprovision of several sets of delay networks to enable several outputs tobe steered independently for different directions of reception.

A further prior proposal employs a plurality of aerials arranged to`form a circular pattern and comprising diametrically disposedintersecting rows of spaced aerials having individual means disposedbetween each aerial and one or more receivers or transmitters common toall the aerials yfor adjusting the time differences between the outputfrom or input to the individual aerials, the adjustments for any givendirection of reception or transmission being eifected by a commoncontrol. According to the said further prior proposal the severaloutputs of the aerials of each row are fed to an adjustable delay unitcommon to the row and the signals from the adjustable delay units, whichcorrespond in number 4tothe number of rows of aerials, are combined.

According to the present invention, a steerable directional aerialsystem comprises an array of spaced aerials distributed over the area ofthe array, means for grouping selected aerials `for receiving a signalof given frequency and direction of arrival, 'the `aerials being dividedinto groups according to the space distribution thereof andV thefrequency and direction of arrival of the signal, means for shifting thephases of the outputs of all the aerials in a group by the same amount,and means for combining :the phase-shifted outputs of the groupedaerials lfor feeding to a receiver.

y Preferably the -aerials are distributed irregularly over the site areawhich itself may be irregular in shape. In this way a maximum offlexibility is obtained in laying out the aerial system. Also, anirregular distribution of4 the aerials leads toa reduction of minorlobes in the polar diagram of the system.

The phases of the outputs of the aerials for a given signal may berepresented on a vector diagram in which the vectors, each of whichrepresents the output of an aerial, radiate from a common point. Bydividing a circle centred on such common point into sectors and byshifting the phases of all the vectors in each sector by a fixed angledetermined by the mean angular displacement of the sector from areference direction, the

resultant response of the aerials can be made sutliciently close forpractical purposes to the ideal system in which the output of eachaerial is phase-shifted according to the angular position of the vectorrepresenting the output of the aerial, with respect to the saidreference direction.

According to a further feature of the invention therefore, the vectorsrepresenting the outputs of the aerials are grouped into a plurality ofequal sectors and the outputs of the aerials represented by the vectorsin selected sectors are lall shifted in phase by a iixed angledetermined by the mean angular displacement of the respective sectorfrom a reference direction thereby to bring the vectors of said selectedsectors within the sector containing the said reference direction.

The invention will now be described with reference to the accompanyingdrawings, in which:

FIGURE 1 is a diagrammatic representation of an aerial array suitablefor carrying the invention into effect;

FIGURE 2 is a vector diagram of the respective outputs o-f the aerialsof the array;

FIGURE 3 is a vector diagram illustrating a method of phase displacementbased on two-sector phasing;

FIGURE 4 is a vector diagram illustrating a method of phase displacementbased on four-sector phasing;

FIGURE 5 is a schematic diagram of one form of 'steerable directionalaerial system according to the invention;

FIGURE 6 shows an alternative arrangement of the system of FIGURE 5;

FIGURE 7 shows a portion of a punched tape for coutrolling the operationof the system; and

FIGURE 8 is a circuit diagram of control means operable by the punchedtape of FIGURE 7.

Referring rstly to FIGURE l, the aerial array shown therein comprises aplurality of unit aerials 1 which are identical and may be regarded, forthe purpose of vector analysis, as omnidirectional point sources, andalthough in the drawings only a limited number of aerials is shown, inpractice there will be many more, for example P aerials. Aradio-frequency wave having a plane wave front `and incident on thearray of aerials 1 i-s shown at 2.

The phase of the output of any one of the aerials 1 relative to theoutput of a hypothetical reference aerial, for example a referenceaerial positioned at the centre of a circ-le 1a enclosing the array, isa function of the direction in azimuth and elevation from which the wave2 aproaches, the position of the aerial in the array, and the frequencyof the radio-frequency wave. The said output phase for each aerial maybe denoted by p, Where -1r q5 +1r, and since the array of aerialscomprises a large number of irregularly disposed aerials thecorresponding values of the angle la for the various aerials may' beassumed to be randomly distributed as shown in the vector diagram ofFIGURE 2., in which the arrows 3 represent the relative phase angle ofthe outputs of the aerials 1 of FIGURE l.

In FIGURE 3 the outputs of the individual aerials are grouped togetheraccording to their phases relative to the reference direction in thefollowing manner:

,Group .Af-Outputs for which fp is in the range 0 to +0. Thecorresponding aerials are designated the A` aerials and their numberwill be denoted by a.

Group B Outputs for which o is in the range +0 to (1r-0). Thecorresponding aerials are designated the B aerials and their number willbe denoted by b.

Group C.--Outputs for which qa is in the range (1r-0) to fr or the range-vr to (f1-1r). The corresponding aerials are `designated the C aerialsand their number will be denoted by c. j

Group D.-Outputs for which is in the range (t9-1r) 3 to 0. Thecorresponding aerials are designated the D aerials and their number willbe denoted by d.

It will be apparent that the direction of arrival (in azimuth andelevation), the frequency of the incoming signal and the position of theaerial in the array will determine in which group an individual aerialwill be included.

IIf now the outputs of all the C aerials are rst changed in phase byangle 1r so that the outputs of the C aerials lie within the range to+0, i.e. within the range of the group A aerials, and the outputs of theC aerials are then combined with the outputs of the A aerials, thereresults a single output indicated in FIGURE 3 by ER which is angularlydisplaced from the reference vector E0 which represents the resultantoutput from an ideal system in which the output of each individualaerial is changed in phase so that the outputs are precisely in phasebefore they are combined. In the method of combining illustrated inFIGURE 3 the outputs of the B and D group aerials are discarded so thatthe system may be termed to a two-sector system, since only the outputsof the A and C group aerials are utilised. Thus, in FIGURE 3 EArepresents the resultant of the outputs of the A group aerials and ECand E'C respectively represent the resultant of the outputs of the Cgroup aerials before and after the phase change.

It is desired to find the magnitude of the resultant ER of adding theoutput of all the A and C aerials together (i.e. of adding EA and EC),and then to compare this with the magnitude of the EO. Since P isassumed to be large, a substantially uniform average density of vectorsrepresenting aerial outputs exists within the sector 0 to +0 (providedthe elemental sectors compared for equality of vector density are nottoo small); therefore the phase of ER closely approaches that of thereference vector EO and it can be readily shown that ER=e a. `il w (l)where e is the amplitude of the output of each unit areial.

Furthermore, since P is large, an inspection of the diagram shows thatEquation 4 above enables the response of a simple twosector system inwhich 0 has any arbitrary value to be compared with that of an idealisedsystem, i.e. one in which all the aerials are used and no phase errorsoccur, and by choosing a value of a two-sector system which uses all theaerials is obtained, and for such a system i.e. the theoretical responseof a two-sector system in which all the aerials are used would be 3.92decibels below that of an idealised system.

The two-sector system with just described, divides the vectorsrepresenting all the aerial outputs into two groups corresponding to twosectors of angular width 1r, and those in one group are changed in phaseby 1r before all aerial outputs are added. This is a particular form ofthe generalised sector system in which the output vectors are dividedinto T equal groups such that all the vectors in any one group liewithin a sector of angular width 21r/ T; the outputs in each groupexcept one are then changed in phase by the appropriate multiple of 21r/T to bring all the outputs into said one group and all outputs added. Itcan be shown that, provided T is fairly small (thus ensuring a uniformaverage density of vectors throughout each sector) Efo w; S111 where Eris the resultant obtained by bringing into phase the resultants of thevectors in each sector.

The following table shows the value of ET/EO for various values of T.

The table shows that with a system using only four sectors as shown inFIGURE 4 it is theoretically possible to achieve an output which is lessthan one decibel below that of an idealised system.

Referring now to FIGURE 5, there is shown one form of practicalembodiment of a four-sector system according to the invention in whichthe output of each aerial 1 to P is fed through an amplier 4 and a-distribution network 5 to a plurality of four-way switches 6corresponding in number -to the number of receivers 1 to Q (not shown).From each lfour-way switch there are four connections to four widebandphase-shift networks 7, 8, 9 and 10 for introducing relativephase-shifts of 0, 1r/2, 1r, and 31r/2 respectively, the outputs fromthe yfour phaseshift networks being fed to a combining network 11 andthence to the receiver. It will =be apparent that by means ofthefour-way switches 6 the outputs of the aerials may be connected in fourgroups each group characterised by a relative phase-shift of 0, 11F/2,1r, and 3w/ 2 respectively, the four-way -switches being yoperated lby adirection control 12 which-depcnding on the frequency and direction of`arrival (in azimuth and elevation) of a signaloperates the switches togroup the aerials for connection to the phase-shift networks to give therequired phase adjustment before combining the aerial outputs. It willbe appreciated that since it is not known to make la widebandphase-.shift network having a constant phase-shift at all frequencies itis necessary to provide in each group a network having a phase-shiftwhich differs -from those in other groups by constant amounts. One ofthese groups can be looked upon as .the datum with a relativephase-shift of 0 while the others have phase-shifts of 11'/ 2, 1r and31r/ 2 relative to that in the datum group.

In the :alternative arrangement of FIGURE 6, the elements are arrangedsimilarly to that of FIGURE 5 with the exception that the widebandphase-shift networks 7a, 8a, 9a and 10a are introduced into each aerialcircuit before connection to the four-way switches. Thus, the four-wayswitches 6a of FIGURE 6 have four connections to each aerial circuit andone connection to the corresponding receiver, whereas the vfour-wayswitches 6 of FIGURE 5 have one connection to the 4aerial circuit andfour connections to the receiver.

In the four-sector switching system described above with reference toFIGURES S and 6, only one of the four phase-shift networks is connectedat a time `but it will be apparent that by simultaneously connecting twonetworks corresponding to adjacent 'sectors there would result aphase-shift midway between the two and enable the control system to beoperated on an eight-sector basis. Thus, if the four outlets of thefour-way switches in FIGURE 5 or the four inlets of the switches inFIGURE 6 are designated A, B, C and D respectively, and if the outletsor inlets Iare connected to networks giving relative phase-shifts of 0,1r/2, 1r, and 31r/ 2 respectively then the eight different phase-shiftscan be obtained by utilising A, A and B together, B, B and C together,and so on.

In yet another arrangement a steered-null response may be obtainedinstead of a steered maximum response. For example, in a four-sectorsystem a steerednull response may be obtained by arranging for one halfof the aerial outputs to be shifted in phase by 1r from the phases whichwould be required to give a maximum response. A steered-null response isuseful in direction finding and in the reduction of interference fromunwanted signal-s.

One form of aerial suitable for use in .an array according to theinvention and having the desired radiation and impedance characteristicscomprises an inverted cone yformed by 16 wires equally spaced around thetop of the cone and connected together and to the inner conductor of anaerial feed cable at the base of the cone, the cone being 24 Ifeet 6inches high and 23 feet across the top of the cone. The aerials arearranged irregularly within the array :but a sufliciently uni-formdensity of aerials is provided to ensure representative sampling of anincoming signal over the array aperture. Thus there may be between 50and 100 aerials for an array having an aperture of -from 300 to 400metres in diameter.

The four-Way switches each comprises four parallel radio-frequency pathseach of which may include an electronic element, `for example thermionicvalve, solidstate diode, or a transistor, which may be operated from onestable condition =to another to make the transmission loss in the pathvery large or very small respectively. Operation -of the said electronicelement is controlled by a conversion and memory circuit which convertsinstructions received from the direction control system, for example in-the `form of pulses, into a form suitable for operating the electronicelement and `to maintain such operation until subsequent instructionsare received.

The direction control system is required to translate the operationalrequirements yfor each receiver as specied in terms of frequency anddirection of arrival (in azimuth and elevation) of a signal into-corresponding instructions to .the switches associated with a givenreceiver.

In computing the instructions .for the switches it is required lirstlyto calculate the phase angle :p of the output of each aerial for signalsof given wavelengths, azimuthal bearings, and elevational angles andthen to determine lthe phase-shift required `for each -aerial whenreceiving signals of each wavelength, azimuthal bea-ring andeleva-tional angle.

The basic equation used to decide the phase angle 11) of the current ina given aerial relative lto the current in Aan aerial at the centre ofthe -array is given by qsr=sr cos (or-9,) cos where Sf=distance of thegiven aerial `from centre. 01r=bearing of the given aerial from centre.ly=waveler1gth of signal.

=azimuthal bearing of signal. =elevational angle of signal.

Lf the result is This procedure must be carried out for each aerial inthe array and for each Wavelength and direction of arrival and althoughthe bearing of a station may be known and the angle of elevation foundfrom the characteristics of the ionosphere, variations in the ionospheregive rise to changes in bearing and elevation. Thus, even to receive onestation, it is necessary to calculate several sets of sector-switchinginstructions and in view of the large number of calculations involved toprovide switching instructions for receiving a number of differentlydirected signals the calculations are preferably made by means of anelectronic computer and the results recorded for subsequent use incontrolling the operation of the switches. Conveniently, the computer isprogrammed in such a manner that the output is obtained in a formsuitable for recording on a tive-unit punched tape which is thenemployed to control directly the operation of the switches of afour-sector system as described with reference to FIG- URE 4. Otherrecords such as, for example, a magnetic tape, may also be used.

A portion of one such punched tape is shown at 13 in FIGURE 7 in Whichthe characters indicate sector-phasing instructions for the respectiveaerials. The first character indicated by the punched hole 14 is a resetcharacter for resetting the electronic switches as will hereinafter bedescribed. A punched hole in the second position as indicated at 15indicates that the phase of the corresponding aerial leads that of thehypothetical reference aerial by an angle of between 0 and '1r/2 andthat therefore no phase-shift is necessary; while a punched hole in thethird position 16 indicates a lead in the phase of the correspondingaerial of between 1r/ 2 and 1r and that therefore a lag of 1r/2 must begiven by the phase-shift network in order to shift the vectorrepresenting the output of the aerial to the required sector of thevector diagram.

The tape of FIGURE 7 is used to control the operation of the Switchesand one form of tape-controlled switch is shown diagrammatically inFIGURE 8. In this arrangement the tape is caused to pass under peckersP1, P2, P3, P4, P5, which are arranged to scan the lines of holes in thetape and to make contact with the positive pole of a direct currentsupply when a hole is encountered. The tape is fed by means of a tapereader feed operated by an electromagnet T which in turn is energisedthrough a motor-driven contact M.

The four peckers P1 P4 are connected respectively to the wipers of fourrotary selector switches S1, S2, S3, S4, which are driven at the samespeed as the tape reader by means of an electromagnet R also energisedfrom the motor-driven contact M. The tape is arranged so that a resetcharacter as indicated by the punched hole 14 in FIGURE 7 precedes thephase-shifting information for each aerial and this character is scannedby the pecker P5 to operate a release electromagnet Z which restores theselectors S1 S4 to their initial or start position.

As the tape is fed forward one step the selectors S1 S4 are alsoadvanced one step to the position shown in FIGURE 8 and according towhether the corresponding pecker encounters or does not encounter a holein the tape toggle relays A, B, C and D connected respectively to thefour switches S1 S4 are operated or not operated. Thus, and againassuming the tape to be punched as shown in FIGURE 7, the secondcharacter 15 will cause relay B to be operated through the pecker P2 andswitch S2. Contact B1 of relay B closes a holding circuit for the relaythrough a contact Y2 of a relay Y connected in parallel with the releasemagnet Z. Relay B at its contact B2 closes a circuit to open a normallyclosed diode gate DG2 to permit the output from the aerial 1 to passthrough capacitor K2, gate DGZ to the required phase-shift network, 7,8, 9 or 10 of FIG- URE 5.

The selector Wipers together with the tape are then stepped one step byoperation of the motor-driven contact M and the second character of thetape is read. In

7 the case of the tape shown in FIGURE 7 this is the character 16. Thischaracter will be read by the pecker P4 to cause relay H to be operatedto connect the aerial 2 to the required phase-shift network in a similarmanner to that described above with reference to the operation of relayB.

The stepping of the tape and of the selectors S1 S4 is continued untilall the aerials have been connected to the required phase-shiftnetworks, after which the motor-driven contact M is stopped.

When it is desired to steer the major lobe of the aerial array to a newdirection a new section of tape is read and the rst character thereof isscanned by the pecker P5 which causes the selector release magnet Z tooperate to restore the selectors to their initial position and alsooperates relay Y which opens its contacts to release the previouslyoperated and locked-up toggle relays.

It will be understood that although a switching control system employingelectromagnetic switches has been described, the invention is notlimited to such an arrangement and that electronic switching elementsmay be employed to carry out the functions of the selector switches S1S4 and associated relays described with reference to FIGURE 8.

I claim:

l. A steerable directional aerial system comprising an array of spacedaerials distributed over the area of the array, said aerials havingoutputs of different phase upon reception of a signal of given frequencyand direction of arrival, the aerials being divided into groupsaccording to the space distribution thereof and the frequency anddirection of arrival of the signal such that the aerials in each grouphave outputs the phases of which lie within limits corresponding to theparticular group, means for shifting the phase of the outputs of all theaerials in each group by a predetermined amount which is the same forthe aerials for any group but which differs from group to groupdepending upon the mean phase displacement of the group with respect tothe phase of a reference group, and means for combining thephase-shifted outputs of the groups of aerials for feeding to areceiver, each aerial being connected to a plurality of switching meanseach adapted to connect the aerial through a selected one of a pluralityof phase-shift networks to a separate receiver associated with oneswitch means of each plurality of switching means there being thus aplurality of receivers corresponding in number to the number of saidplurality of switching means, whereby upon operation of a switch meansin each plurality of switch means associated with one receiver theoutput of each aerial is shifted in phase in accordance with thecharacteristics of the phase-shift network selected by each switchmeans.

2. A steerable directional aerial system comprising an array of spacedaerials distributed over the area of the array, said aerials havingoutputs of different phase upon reception of a signal of given frequencyand direction of arrival, the aerials being divided into |groupsaccording to the space distribution thereof and the frequency anddirection of arrival of the signal such that the aerials in each grouphave outputs the phases of which lie within limits corresponding to theparticular group, means for shifting the phase of the outputs of all theaerials in each group by a predetermined amount which is the same forthe aerials for any group but which differs from group to groupdepending upon the mean phase displacement of the group with respect tothe phase of a reference group, and means for combining thephase-shifted outputs of the groups of aerials for feeding to areceiver, the receiver being connected to a plurality of switching meanseach adapted to connect the receiver through a selected one of aplurality of phase-shifting networks to an aerial associated therewith,the number of switching means thus corresponding in number to the numberof aerials, whereby upon selective operation of each switching means inthe said plurality of switching means the output of each aerial isshifted in phase in accordance with the characteristic of thephase-shifting network selected by its associated switching means.

3. A steerable directional laerial system comprising an array ofirregularly spaced aerials distributed over the area of the array, saidaerials having outputs of different phase upon reception of a signal ofgiven frequency and direction of arrival, the outputs being representedby vectors, the aerials being divided into groups in which the outputvectors lie within the limits of corresponding sectors, phase shiftermeans associated with the aerials of each group for shifting the phaseof the outputs of the aerials of the respective groups, each phaseshifter means having several predetermined selectable values of phaseshift corresponding :to the mean phase displacements between thecorresponding sector and different reference phases, means for selectingthe phase shift values of the respective phase Shifters to shift themean phase of said sectors to the same reference phase, and means forcombining the phase shifted outputs of the groups of aerials.

References Cited in the file of this patent UNITED STATES PATENTS 4',1,738,522 Campbell Dec. 10, 1929 0 2,245,660 Feldman et al. June 17,19141 2,432,134 Bagnall Dec. 9, 1947 2,444,425 Busignies July 6, 19482,466,354 Bagnall Apr. 5, 1949 2,510,280 Goddard June 6, 1950 FOREIGNPATENTS 168,845 Austria Aug. 25, 1951 496,027 Great Britain Nov. 23,1938 545,052 Great Britain May 8, 1942

